A known water pump applied to a water-cooled engine includes an impeller provided on an end of a rotational shaft supported by a body via a bearing, and cooling water is circulated in an engine by rotating the rotational shaft. A space is formed between the bearing and a mechanical seal which is provided between the impeller and the bearing. Vaporized cooling water infiltrates the space via the mechanical seal and is condensed into water drops, and the condensed water drops are drained through a draining hole to a reservoir provided at a bottom portion of the body. A groove which introduces the water drops leaked to the draining hole to the bottom of the reservoir is provided at a sidewall of the reservoir. Further, an annular groove is provided at a sidewall of the reservoir so that the leaked cooling water stored in the reservoir is not drained to the atmosphere side. (I.e., disclosed in JPH11-336699A)
According to another known water pump disclosed in JP2004-108250A, a stepped portion is provided between a vapor hole and an opening surface where the draining hole opens to the reservoir, so that the vapor hole positions above the opening surface, and draining of the water drops leaked from the draining hole to the atmosphere side via an upper surface of the vapor hole is prevented.
However, with the constructions of the water pump disclosed in JPH11-336699A and JP2004-108250A, there is a drawback that the leaked water stored in the reservoir rises upward because of capillary action at a minor gap between a plug which plugs an opening portion of the reservoir and a body to which the plug is press-fitted, so as to drain to the outside through the vapor hole.
A need thus exists for a water pump which is not susceptible to the drawback mentioned above.